1. Field of the Invention
This invention relates to plasma etching of metals and metal oxides, particularly platinum-family metals and metal oxides.
2. Brief Description of the Background Art
There is presently demand for processes by which metals and metal oxides can be etched, particularly those metals and metal oxides that are both conductive and relatively inert to oxidation.
For example, in the field of semiconductor integrated circuits, digital information storage and retrieval technology plays an important role in the advancement of modem digital electronics. Memory size and access time frequently serve as measures of progress in this technology. Present state-of-the-art memory devices include small-feature-size high-density dynamic random access memory (DRAM) devices, which use high-capacitance storage capacitors containing high dielectric constant materials as memory array elements. The high dielectric constant materials, or ferroelectric materials, are made primarily of sintered metal oxide and contain a substantial amount of highly reactive oxygen. To form storage capacitors with such ferroelectric materials, the electrodes should be composed of materials with reactivities that are sufficiently low to prevent oxidation of the electrodes, which oxidation would decrease the capacitance of the storage capacitors. Therefore, platinum family metals (i.e., platinum, iridium, ruthenium, palladium, rhodium and osmium) and their conductive oxides are preferred materials for use in the manufacture of capacitors for high-density DRAM devices.
Etching such materials poses various new challenges. For example, commonly assigned WO 00/49650 discloses a technique for etching a layer of platinum or iridium within a wafer by heating it, while exposing it to a high-density inductively coupled plasma of an etching gas that comprises chlorine, oxygen and argon. Although such chemistry is effective to etch electrodes with desirable properties (e.g., small feature sizes and substantially vertical sidewalls), the by-products of this process can be quite difficult to remove from the inside surfaces of the reactor chamber, frequently requiring very aggressive removal measures. For example, aqua regia (i.e., a mixture of nitric acid and hydrochloric acid) is typically used to remove the by-product deposits from the chamber surfaces. Furthermore, the by-product deposits have significant conductivity, which is problematic with respect to dielectric reactor components (e.g., dielectric ceilings of inductively coupled plasma reactors), because the dielectric properties of these components are degraded upon deposition of the conductive material, causing etch rate instability, among other effects.
The above and other drawbacks associated with the prior art are addressed by the processes of the present invention. According to an embodiment of the invention, a method is provided which comprises: (1) providing a wafer, which wafer further comprises (a) a semiconductor substrate, (b) a metal or metal oxide layer over the semiconductor substrate, and (c) a titanium containing patterned mask layer having one or more apertures formed therein positioned over the metal or metal oxide layer; and (2) etching the metal or metal oxide layer through the apertures in the mask layer by a plasma etching step, which is conducted using plasma source gases comprising the following: (a) a gas that comprises one or more chlorine atoms and (b) a gas that comprises one or more carbon-oxygen bonds.
The gas that comprises one or more carbon-oxygen bonds is preferably CO gas and/or CO2 gas, while the gas that comprises one or more chlorine atoms is preferably Cl2 gas, carbon tetrachloride gas, silicon tetrachloride gas and/or boron trichloride gas.
In some preferred embodiments, the gas that comprises one or more carbon-oxygen bonds is CO gas, while the gas that comprises one or more chlorine atoms is Cl2 gas. In this instance, the ratio of CO gas to Cl2 gas preferably ranges from 1:1 to 15:1.
In other preferred embodiments, the plasma source gases further comprise O2 gas, N2 gas or both. Where present, the O2 gas is preferably provided in an amount ranging from 0.1% to 20% and the N2 is provided in an amount ranging from 0.1% to 10%.
In still other preferred embodiments, the plasma source gases further comprise one or more noble gases selected from argon gas, krypton gas and xenon gas.
The plasma-etching step is preferably conducted in a high-density plasma at a pressure ranging from 5 to 50 mTorr. Wafer temperatures preferably range from 250 to 550xc2x0 C. during the plasma-etching step.
The following materials are preferred: (1) the semiconductor substrate is preferably a silicon substrate, (2) the metal or metal oxide layer preferably comprises one or more metals selected from platinum, iridium, ruthenium, palladium, rhodium and osmium, or one or more metal oxides selected from iridium oxide and ruthenium oxide, and (3) the titanium containing mask layer preferably comprises one or more compounds selected from titanium metal, titanium oxide and titanium nitride.
In some embodiments, the wafer further comprises: (a) a semiconductor oxide layer disposed on he semiconductor substrate, and (b) a barrier layer disposed between the semi conductor oxide layer and the patterned masking layer, wherein the barrier layer is preferably selected from a titanium layer and a titanium nitride layer.
According to yet another embodiment of the invention, a method is provided which comprises: (1) providing a wafer that comprises (a) a semiconductor substrate, (b) a platinum family metal layer over the semiconductor substrate, and (c) a patterned masking layer having one or more apertures formed therein which comprises titanium, titanium oxide or titanium nitride positioned over the platinum family metal layer; and (2) etching the platinum family metal layer through the apertures in the mask layer by a plasma etching step that is conducted using plasma source gases comprising Cl2 gas and CO gas. In this embodiment, the wafer is heated to a temperature ranging from 250 to 550xc2x0 C.
One advantage of the present invention is that a method is provided by which metals and metal oxides, including platinum family metals and metal oxides, can be etched.
Another advantage of the present invention is that such materials can be etched while providing (a) acceptable selectivity with respect to the masking layer, (b) good etch rate stability, and (c) repeatable and relatively vertical etching profiles.
Another advantage of the present invention is that a method is provided in which metals and metal oxides, including platinum family metals and metal oxides, can be etched while providing by-products that have very low conductivity.
Yet another advantage of the present invention is that a method is provided in which metals and metal oxides, including platinum family metals and metal oxides, can be etched while at the same time providing by-products that can be easily removed from interior reactor surfaces.
The above and other embodiments and advantages of the present invention will become immediately apparent to those of ordinary skill in the art upon reading the detailed description and claims to follow.